There are two things,
- Will it work?
- Is it supported?
Will it work?
As for whether or not it'll work, your only concern should be is the fitting valid for the type of tubing. In the case of Uponor they support,
Basically it boils down to this, a manufacturer certifies specific type of fitting and rings or clamps for their tubing, (or doesn't and uses totally proprietary parts like SharkBite.) In the case of Pex A, Uponor, most plumbers now seem to use F1960 which is commonly called expansion or "cold expansion" (since no heat is required). With a battery-powered tool these are the best simply because there is little room for user-error.
Your fittings sound like they're ASTM F1807 and not cold expansion because you have a stainless steel ring.
Is it supported?
When it comes to mixing non-Uponor fittings into your plumbing system, according to the Uponor Warranty, and all PEX manufactures basically have the same warranty: Uponor Pipe with non-Uponor fittings reduces your warranty from 25 years, to 10 years.
What would I do
I now want to add a tee for a hose bib
I would just ignore what other fittings you have in the house and use F1960 expansion. It makes everything easy. It's all around better. Upfront cost on a battery-powered expansion tool is worth it for me, it's an insurance policy in the event you have a freeze and want to fix things in 5 minutes.